Process of making cellulose acetate with vaporized acetylating agents



Oct. 4, 1932. c. R. NOLLER 1,88@,466

PROCESS OF MAKING CELLULOSE ACETATE WITH VAPORIZED ACETYLATING AGENTS Filed Feb. 2. 1928 75 Vacuum un/o Jwwntw,

CZIIL R. N01191:

atbmmg Patented Oct. 4, 1932 UNITE-D srArrEs "PAT. as

can]; R. nonun on-Recliners; NEW YORK,ASSIGNOR To EASTMAN KODAK, COMPANY, or rm'ennswnmnnwwonx; A CORPORATION or NEW YORK,

rRocEss. OF MAKING cnLLunosE ACETATE wrria'vAroniznn AcErYLATIivG AGENTS Application filedFebruary 2, 1928."Seria1 No. 251,297.

This invention relates t'oprocesses of making cellulose acetate using vaporized acetylating agents. ()ne object of theinve-nti'on is v to provide a process-of this nature which the desired acetylationof cellulosic materials can be effected within a useful time, and yet the product will not be seriously degraded nor contaminated with ui-iacetylated fibers.- Other objects will hereinafter appear. 3e In the accompanying drawing'the single figure is a diagrammaticsectional viewon an exaggeratedscale of onetype of apparatus in which my process may be carried out. In U. S. Patent No.'1,030,31-1,-.Koetschet r5 andTheu-mann,June25,1912EAcetylation of cellulosic materials there is disclosed a proc ess of making' cellulose acetate in which acetic anhydrid' vapors are passed through cotton from a vaporizer to a condenser. The syst'em may be under sub-atmospheric pressure in order to assist the boiling of theiacetic anhydridin the vaporizer: When ili'II'lOIGClllB of acetic anhydrid reacts with amolecule of cellulose there isliberated a molecule of acetic acid. This acid has a boiling 'point always less than that of acetic anhydrid at the same pressure. Consequently, any acetic acid present in the-cotton initially, or formed during the reaction by'the process of said I patent, will beimmediately carr'iedby the stream of acetic anhydrid vapor intothecondenser and liquefied there. l j

I have found that the reaction may be regulated to obtain the desired results men'- tioned above by retaining at least part of the vapor of acetic acid, Iiberatedby the reaction,

in contact with the cellulosic material which is being treated. Since enough of this acid A is rapidly liberated at the 'startof the reaction; to saturate the reactionspace with acetic acid vapor, and to keepit saturated until the material is acetylated,-practically theentire process is carried out by a mixture of saturated vapors of acetic 'anhydridand' acetic acid. Preferablythe air is eliminated from the reaction space, say by evacuating it, prior to conducting the reaction. course, the cellulosic material is mixed with one of the known agents that promotes acetylation. In the preferred form of my invention I do not' employ a streamof the mixed anhydrid and acid vapors, but. merely heat the cellulosic material in a closed vessel containing' an open body or pool of acetic anhydrid. The latter may be in a container above the cellulose to be treated, and'the acetic anhydrid vapors can'difiu'se over the edges of the container downrinto thece'llulosic matee rial. The product, which is obtained in an undissolved' state, retains the original fibrous or other-form of theraw material, and is soluble in chloroform when the'reaction is carried through to completion. I The cellulosicmaterial may be any ofthose heretofore used in making cellulose acetate by the use of acetic" anhydrid in liquid forrn,such as purified cotton wool, tissue paperprepared from clean cotton fibers, surgoal cotton wool, and even bleached sulfite in the prior art with liquid acetic anhyd'rid." I prefer, however, to use liquid agents with which the cellulosic mat'erial maybe readily impregnated, said liquids 'being'of low volatility. relative to acetic anhydrid. Because of their cheapness, sulfuric acid and para: toluene sulfon c acid serve as excellent ex amples.

I shall now describe several examples of my invention, but it willbe understood that the latter is not limited tothef details. thus given, except as indicated in the appended claims. In a closed vessel there is placed 2 parts-by weight of air-dried purifiedcot ton, previously impregnated with of; I its weight of sulfuric acid. "In an open containerin the same closed vessel there isplacedj f 20 partsby weight. otac'etic anhydrid.{ From the closed vessel'the jairis exhausted until: I

arelativelyhighgvacuum is reached, say pressure of 10' millimeters of mercury; The' vessel and its contents are then heated to 60 to 65 C. and kept at that temperature until the reaction has proceeded to the desired point. When the contents are heated, as mentioned above, the vapors of acetic anhydrid rapidly evolve in. the closed vessel and come in contact with all of the exposed surface of the cotton containing the catalyst. The reaction then starts and acetic acid is formed, which vaporizes and mingles with the acetic anhydrid vapors throughout the closed vessel, thus remaining in contact with the cotton throughout the rest and main part of the reaction. Moreover, the aceticiacid vapor rapidly reaches saturation and remains saturated throughout the reaction. The end point of the reaction isfound by taking samples from time to time and testing their solubility in chloroform, or in a mixture of equal parts of chloroform and alcohol. Un-

der the conditions just given, full solubility has beenobtained, together with an acetyl content of 43.9% in as short a time as 39 hours. V

In still'another example of my invention, 100 parts by weight of air-dried purified cotton is impregnated with 1% of its weight of paratoluene sulfonic acid. This'is placed in a vessel containing, above it, an open receptacle in which there is 280 parts by weight of acetic anhydrid (95%.strength). The vessel is carefully sealed and the 'air'removed by a preliminary evacuation down to about a pres sure of millimeters of mercury. The interior of the vessel, including the cotton and r the acetic anhydrid, is kept at ,to C., until the desired solubility and acetyl content is reached jinthe product. 'Under such conditions there is obtained fully chloroformsoluble fibers after about 7 2 hours. It is one of the features of this process that it is economical of anhydrid and only slightly more than the theoretical amount required for the acetylation is consumed. I'prefer to have the receptacle containing the acetic an- ".hydrid above the cotton in the closed vessel,

ratherthan below it, because a much 'more even diffusion of anhydrid is obtained, with a consequent uniform acetylation throughout the cotton. Where the anhydridis below the cotton, the lower layers of the latt er become completely acetylated'before the portions at the top. I

Referring. to the accompanying drawing, 1 indicates a closed vessel composed of or lined with any suitable material which is resistant'to the vapors of acetic anhydrid and acetic acid under the conditions stated above. This vessel may be heated in any suitable manner, say by a 'jacket 2 through which thereis circulated a suitable heating fluid,

which enters through pipe '3 controlled by valve 31 and leaves throughpipe 4 controlled by valve 41. The cover 5 ofthei vessel 1 is rest of vessel 1 by any of the usual means, such as the swinging bolts 6. Leading from the top of cover 5 is a pipe 7, controlled by valve 71, which leads to the vacuum apparatus. Within/the vessel 1 in the upper part thereof is a support 8 upon which ,there is an open-receptacle 9 in which there is a body of liquid acetic anhydrid 10. Below the receptacle '9 there is located the cellulosic material, such as cotton 11. The vapors ris ing from anhydrid 10 diffuse down and through the cotton 11 and become mingled with the vapors of acetic acid liberated in the reaction, as described above in connection with the examples;

Having thus described my invention, what I claim as new and desire to secure by Let ters Patent is: v p a 1. In the process of making cellulosecacetate, placing cellulosic fibers, impregnated with an agent which promotes acetylation, in

part of an enclosed space, placing an open.

tents. of said space until said fibers are acetylated. V

2. The process of producing cellulose acetate which comprises introducing cellulosic material, liquid acetic .anhydride and a catalyst into an enclosed vessel and maintaining said vessel at least partially evacuated until the cellulose has become acetylated. v 3. v The process of producing celluloseacetate. which comprises introducing liquid acetic anhydride and cellulosic- .material which hasbeen impregnatedwith an agent that promotes acetylation into an enclosed vesselrand maintaining said vessel at least partlally evacuated until the cellulose has become acetylated.

4 The process of producing cellulose acetate which comprises introducing cellulosic material, liquid acetic anhydride and a catalyst into anenclosed vessel, and heating the vessel and maintaining it at least partially evacuated until the cellulose has become acetylated.; V c

' 5. The process of producing cellulose acetate which comprises introducing liquid acetic anhydride and cellulosic material which has been'impregnated with an agent that promotes 'acetylation. into an enclosed ,Vessel, and heating the vessel and maintaining it at least partiallyevacuated until the cellulose has become acetylated.

Signedat Rochester, New'Yorkthis 28 day of January 1928. p 7 1 CARL R. NOLLER.

detachably held gas-tight; contact with the V I 

